Supplemental Inflatable Restraint (SIR) systems are widely used in motor vehicles. Controllers for use in such SIR systems should be robust and immune to unwanted deployment. A velocity boundary curve (VBC) algorithm is used in an electronic crash sensor in the above U.S. patent application Ser. No. 07/797,850 for detecting a high speed pole impact early in a crash event. The sensor disclosed therein utilizes acceleration signals measured by a micro-machined accelerometer located in the controller that is mounted in the vehicle passenger compartment as illustrated in FIG. 1. In order to achieve timely discrimination, the VBC utilizes four threshold curves digitized and stored in calibration lookup tables. The acceleration signal is digitized, then transformed into forms of jerk, acceleration, and velocity that are compared to four boundary curves that represent thresholds for absolute integral of jerk, partial energy, occupant-to-vehicle relative velocity, and a reset velocity parameter. These four thresholds are values that are based on the deployment and non-deployment crashes, rough road signals, and abuse signals used for calibration.
In the above U.S. patent application Ser. No. 07/798,487, a method of discriminating between air bag deployment and non-deployment events based on vehicle acceleration data is disclosed. When vehicle acceleration data reaches a threshold indicative of the onset of an event, a velocity computation cycle is initiated which computes velocity by integrating the acceleration data and comparing the velocity each millisecond during the cycle with data from a time dependent velocity boundary curve which separates low severity and high severity events in the velocity versus time domain.
Current acceleration-based algorithms exhibit some sensitivity to random noise and vibration events. Also, large signal band charges can dominate oscillation calculations of such algorithms. These changes can occur in low speed angle and pole events. Some applications show some sensitivity to rough road and abuse triggering, thereby requiring relatively high velocity boundary curve levels.